DOI: 10.1002/adfm.200800528 High-Conductivity Polymer Nanocomposites Obtained by Tailoring the Characteristics of Carbon Nanotube Fillers** By Nadia Grossiord, Joachim Loos, Lucas van Laake, Maryse Maugey, Ce´cile Zakri, Cor E. Koning, and A. John Hart* 1. Introduction The electrical conductivity of composites made of a conductive phase dispersed in an insulating matrix critically depends on the filler loading, as described by percolation theory. [1,2] At a low filler concentration, the fillers are present as small clusters or individual elements; since the average distance between the filler elements exceeds their size, the conductivity of the nanocomposite is very close to that of the pure insulating matrix. When a sufficient amount of filler is loaded, a ‘‘percolation’’ path of connected fillers forms and allows charge transport through the sample. At this critical concentration, called the percolation threshold, the conduc- tivity suddenly and rapidly increases. Based on geometrical considerations, the value of the percolation threshold is expected to be strongly influenced by the aspect ratio (ratio of length-to-diameter) of the filler particles. [3–6] Considering a filler system having a particular filler orientation, the percolation threshold decreases with increasing aspect ratio of the filler. Carbon nanotubes (CNTs) are an attractive filler for making electrically conductive nanocomposites, since CNTs possess an excellent conductivity (10 5 –10 8 Sm 1[7,8] ), combined with a high aspect ratio (reaching 100–1000 for mm- long single-wall and multi-wall CNTs). [9–12] These composites are attractive for use in electromagnetic interference (EMI) shielding and electrostatic discharge (ESD) coatings, and as thin-film field-emitters and (at low CNT contents) transparent conductors. [13–15] Abundant literature on conductive CNT/polymer nano- composites presents a striking variation in measured values of FULL PAPER [*] Prof. A. J. Hart Department of Mechanical Engineering, University of Michigan, 2278 GG Brown 2350 Hayward Street, Ann Arbor, MI 48109-2125 (USA) E-mail: [email protected] Dr. N. Grossiord, [+] Dr. J. Loos, Prof. C. E. Koning Dutch Polymer Institute P.O. Box 902, 5600 AX Eindhoven (The Netherlands) Dr. N. Grossiord, Prof. C. E. Koning Laboratory of Polymer Chemistry, Technical University of Eindhoven P.O. Box 513, 5600 MB Eindhoven (The Netherlands) Dr. J. Loos Laboratories of Polymer Technology and Materials and Interface Chemistry Technical University of Eindhoven P.O. Box 513, 5600 MB Eindhoven (The Netherlands) L. C. van Laake [++] Department of Mechanical Engineering, Technical University of Eindhoven P.O. Box 513, 5600 MB Eindhoven (The Netherlands) M. Maugey, Dr. C. Zakri Centre de Recherche Paul Pascal–CNRS Avenue A. Schweitzer, 33600 Pessac (France) [+] Present address: University of Warwick, Department of Chemistry, Coventry CV4 7AL, UK. [++] Present address: Oce ´ Technologies BV, PO Box 101, 5900 MA Venlo, The Netherlands. [**] This work is part of the research program of the Dutch Polymer Institute (DPI), project # 416. The work of John Hart was partially supported by a graduate fellowship from the Fannie and John Hertz Foundation. CNT growth was performed at MIT, where facilities were built and maintained using grants from the MIT Deshpande Center for Technological Innovation and the National Science Foundation (DMI #0521985), and lab space was provided by Prof. Yet-Ming Chiang and Prof. Brian Wardle. The authors are thank Hans Miltner (Free Uni- versity of Brussels, Belgium) for performing the TGA measurements, as well as Prof. Philippe Poulin (Centre de Recherche Paul Pascal, CNRS, Pessac, France) for enlightening discussions regarding this research. We present a detailed study of the influence of carbon nanotube (CNT) characteristics on the electrical conductivity of polystyrene nanocomposites produced using a latex-based approach. We processed both industrially-produced multi-wall CNT (MWCNT) powders and MWCNTs from vertically-aligned films made in-house, and demonstrate that while the raw CNTs are individualized and dispersed comparably within the polymer matrix, the electrical conductivity of the final nanocomposites differs significantly due to the intrinsic characteristics of the CNTs. Owing to their longer length after dispersion, the percolation threshold observed using MWCNTs from vertically-aligned films is five times lower than the value for industrially-produced MWCNT powders. Further, owing to the high structural quality of the CNTs from vertically-aligned films, the resulting composite films exhibit electrical conductivity of 10 3 Sm 1 at 2 wt% CNTs. On the contrary, composites made using the industrially-produced CNTs exhibit conductivity of only tens of S m 1 . To our knowledge, the measured electrical conductivity for CNT/PS composites using CNTs from vertically-aligned films is by far the highest value yet reported for CNT/PS nanocomposites at this loading. 3226 ß 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim Adv. Funct. Mater. 2008, 18, 3226–3234
High-Conductivity Polymer Nanocomposites Obtained by Tailoring the Characteristics of Carbon Nanotube Fillers
Jun 17, 2023
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